Abstract

CD26, or dipeptidyl peptidase IV, is a widely distributed cell surface glycoprotein of approximately 110 kD molecular weight. It is constitutively expressed on a variety of different cell types, particularly on epithelial cells of the intestine, prostate and kidney-proximal tubules1–3. On T cells the expression of CD26 is regulated more stringently. The molecule is absent from the majority of human resting peripheral blood T lymphocytes and is expressed weakly on a fraction of T cells in the blood. Expression increases within two days of T cell activation and increases further after culture in vitro1.2. It has been shown to be a suitable marker for T cells activated in vivo4 and memory T cells have been shown to reside in the CD26+ T cell fraction5. CD26 has several unique properties that distinguish this molecule from related surface proteases:

i.

the expression of CD26 is tightly regulated in different tissues

ii.

it is associated with the differentiation and activation status of different cells